Detergent compositions in tablet form are known in the art, as discussed below, and some products are now on the market. Tablets have several advantages over powdered products: they do not require measuring and are thus easier to handle and dispense into the washload, and they are more compact, hence facilitating more economical storage.
Detergent tablets are described, for example, in GB 911 204 (Unilever), U.S. Pat. No. 3,953,350 (Kao), JP 60 015 500A (Lion), JP 60 135 497A (Lion) and JP 60 135 498A (Lion); and are sold commercially in Spain.
Detergent tablets are generally made by compacting a detergent powder. It has proved difficult, however, to strike a balance between tablet strength and ability to disintegrate and disperse in the wash liquor. Tablets formed using only a light compaction pressure tend to crumble and break up on handling and packing; while more strongly compacted tablets may be sufficiently cohesive but will then fail to disperse to an adequate extent in the wash liquor.
This problem has proved especially acute with tablets formed by compressing spray-dried powders containing anionic detergent-active compounds; these surfactants are otherwise highly desirable because of their good detergency. As the tablet is wetted, highly viscous surfactant gel phases are formed which retard or prevent penetration of water into the tablet interior. In a conventional detergent powder consisting of a a spray-dried base in admixture with other, non-spray-dried components such as bleach, bleach activator and enzyme, anionic detergent-active compounds are normally included in the spray-dried base which constitutes the major proportion of the total powder (and hence tablet) formulation (typically 60-95 wt %). The anionic detergent-active compounds are therefore distributed uniformly and homogeneously through the spray-dried base powder, and widely distributed through the final powder; on compaction, this wide distribution persists into the resulting tablet.
It has now been found that this problem can be substantially alleviated by ensuring that any anionic detergent-active compounds present are not distributed widely through the tablet, but are concentrated in discrete domains within a continuous phase containing little or no anionic detergent-active compound.
EP 355 626A (Henkel) discloses a detergent tablet prepared by compaction of a mixture of at least two powder or granular components A and B, wherein A contains 100 wt % of all anionic detergent-active compound present and B contains 75-100 wt % of all ethoxylated nonionic detergent-active compound present. In the Example, a tablet is produced from a major proportion (50.6 wt %) of component A (a granulated base powder containing 14.42 wt % of anionic detergent-active compound), plus 15.4 wt % of component B, the balance consisting of other non-surfactant components.